Drug administration by the oral route is applicable mostly to low molecular weight (&lt;850 daltons) compounds which are relatively stable at the acidic pH of the stomach and the alkaline condition of the gastrointestinal tract. Bioactive macromolecules, such as insulin (Mol. Wt. 6,000 daltons) which promote growth and control blood sugar level, and the growth hormone somatotropin (Mol. Wt. 22,000 daltons) or the like are inactivated by proteolytic enzymes in the digestive tract, if taken by mouth. As a result, these bioactive macromolecules can be administered only by injection. However injection usually introduces too high an initial dose which is absorbed in part as well as degraded by serious enzymes at the subcutaneous injection site resulting in rapid decay to an inadequately low level a few hours later. To compensate for the decay, a second injection is required. Another remedy to correct the inconsistency is to infuse dilute solution of the labile agent continuously at a low rate. The slow infusion can actually achieve a better outcome, because most active agents have relatively short half-life in vivo or are toxic if the daily required dose is given at once by injection. However, the advantage of low-dose infusion is compromised by the incidence of infection and discomfort due to the presence of the indwelling needle and the catheter attachment. Therefore, extensive effort is continuing to find an implantable infusion device or preparation that can deliver an active agent for a prolonged period of time.